ORIGINAL RESEARCH

Analysis of MW-scale Beam Extraction of EAST Neutral BeamInjector Test-stand

Yongjian Xu • Chundong Hu • Yuanlai Xie •

Jun Li • Sheng Liu • Yahong Xie • Peng Sheng •

Zhimin Liu • Lizhen Liang

� Springer Science+Business Media New York 2013

Abstract Neutral beam injection has been recognized as

one of the most effective means for plasma heating. The

preliminary data of 50 keV, 100 s and 80 keV, 1 s beam

extraction have been obtained on the EAST neutral beam

injector (NBI) test-stand. In this paper, beam energy distri-

bution deposited on each heat load component and neutral

efficiency of EAST-NBI has been measured using water-

flow calorimetry and beam divergence angle and perveance

have been analyzed according to the data obtained from the

thermocouples installed in the calorimeters.

Keywords Beam extraction � Neutral beam �Divergence angle � Perveance

Introduction

Achievement of the ignition of fusion plasmas is one of the

important subjects of plasma heating. It is well known widely

that neutral beam injection (NBI) is the most effective method

for effective plasma heating and has been also verified to be

applicable for current drive [1–4]. As the first full supercon-

ducting non-circular cross section Tokomak in the world,

EAST is used to explore the forefront physics and engineering

issues on the construction of Tokomak fusion reactor.

According to the research plan of the EAST physics

experiment, two sets of neutral beam injector will be built

and operational in 2014. We have achieved to preliminary

experimental results last year [5–7]. So far, the first neutral

beam injector have already achieved 50 keV, 100 s long

pulse neutral beam extraction and 80 keV, 1 s ion/neutral

beam extraction on the EAST-NBI test-stand.

The main purpose of this paper is to analyze beam

energy distribution deposited on each heat load component,

neutralization efficiency and beam divergence angle.

Structure of EAST-NBI and Parameter Setting

The target values of EAST-NBI are that beam energy

50–80 keV, injection beam total power 2–4 MW, beam

pulse width 10–100 s. The photograph of NBI system is

shown in Fig. 1. Main components of the NBI system are

two high-current ion sources, control system, beam diag-

nosis system, vacuum system, gas supply system, cooling

water system and so on as shown in Fig. 2.

In order to calculate the power of extracted beam, water-

flow calorimetry was adopted. Water-flow calorimetry is a

common method to measure high beam power [8–10].

According to the flow and temperature rise of cooling

water in the heat load components, the heat taken away by

the cooling water can be obtained. Ignoring the error, the

energy deposited on the heat load components is equal to

the heat taken away by the cooling water in it.

How to determine the fusion plasma transport accurately

is difficult. Flow balance analysis can be used in confirming

the transport coefficient of plasma. Modulating transport

analysis can obtain the coefficient of diagonal item and non-

diagonal item and remove the uncertainty of source item by

means of modulating source item. The source imposed by

outside can be looked as the modulating source item. Mod-

ulating neutral beam injection is one of the important

methods for part transport analysis. Modulating neutral

beam injection is one of the important methods for part

Y. Xu (&) � C. Hu � Y. Xie � J. Li � S. Liu � Y. Xie �P. Sheng � Z. Liu � L. Liang

Institute of Plasma Physics, Chinese Academy of Sciences,

Hefei 230031, China

e-mail: yjxu@ipp.ac.cn

123

J Fusion Energ

DOI 10.1007/s10894-013-9620-2

transport analysis of plasma. So the EAST-NBI system is

tested in modulating (the duty cycle modulated beam and the

modulation frequency can be adjusted) and non-modulating

beam extraction modes, respectively. Beam extraction sys-

tem consists of four electrodes and power supply system. The

operating parameters of ion source were given in Table 1.

The voltage of four grids and beam pulse width that corre-

sponds to the Table 1 was shown in Table 2.

Ion source works in the parameters above and the

waveforms of each parameter are shown in Fig. 3.

Results and Discussion

Beam carrying energy deposits on each heat load compo-

nents and energy deposition ration has been shown in

Fig. 4. It shows that: (1) at 80 kV, the neutral efficiency is

37.9 %. Generally, the neutral efficiency decreases as

accelerating voltage rise [11]. (2) The energy deposited on

the bending magnet pole shields is higher; it will adversely

affect the long pulse beam extraction. Figure 4 show that

the heat load components are composed of collimators,

Fig. 1 Photograph

of EAST-NBI test-stand

Fig. 2 Schematic view

of EAST-NBI

Table 1 The operating parameters of ion source and bending magnet

Filament

voltage (V)

Filament

current (A)

Arc

voltage (V)

Arc

current (A)

Bending magnet

voltage (V)

Bending magnet

current (A)

Beam extraction

mode

7.6 3,000 86 308 21.5 208 Non-modulating

8.45 2,610 80 1,400 27 263 Modulating

J Fusion Energ

123

bending magnet pole shields, calorimeter (only for mea-

surement) and ion dump. The bending magnet pole shields

and ion dump are main factor affecting the long pulse beam

extraction (the maximum power density of ion dump

and bending magnet pole shields are about 9.5 and

5.04 MW/m2 respectively, the maximum tolerable tem-

perature of heat load component is 350 �C.). In order to

Table 2 The voltage of four grids and beam pulse width

Plasma grid

(PG) [kV]

Gradient grid

(GG) [kV]

Suppressor

grid (SG)

[V]

Exit grid

(EG) [V]

Pulse

width

[s]

50 40 -1,450 0 100

80 64 -1,800 0 1

Fig. 3 The electrical parameters of beam extraction (left: Vacc = 50 kV; right Vacc = 80 kV)

Fig. 4 Beam energy deposition

distribution on the heat load

components (orange magnet

off, blue magnet on;

Vacc = 80 kV) (Color figure

online)

J Fusion Energ

123

take away the heat on them in time, some methods of

enhanced heat transfer were adopted, such as (1) the con-

nection of cooling water tube (ion dump, bending magnet

pole shield) has been changed from series to parallel; (2)

the cooling water of pole shield has been changed from

general bare stainless steel tube to spiral fluted tube.

According to the data obtained from the thermocouple

installed in calorimeter, the temperature difference distri-

bution on the calorimeter can be given [12] (see Fig. 5). The

area (24 cm 9 48 cm) shown in Fig. 5 is the calorimeter

projected area perpendicular to the direction of beam

transmission. The figures on the left show temperature rise

distribution and those on the right are contour plots of

temperature rise at 50, 80 kV, respectively. According to

the data obtained from the thermocouples install in the

calorimeter, the divergence angle can be given.

Beam perveance is a measurement of extracted ions

from ion source for a specific high voltage applied to the

plasma grid. Beam divergence defines the sizes of the beam

along the beamline, which is crucial information for the

requirements of beamline hardware. Figure 6 gives the

relationship between the divergence angle and perveance

and optimum beam perveance. If the ion source is operated

at the optimum beam perveance, the beam divergence

angle is close to the value (0.73� and 1.7�), but there are

some deviations between this value and design value (0.6�and 1.2�) and the next step is to find the reason and solve it.

Conclusion

The waveforms of beam extraction mentioned above show

that EAST-NBI ion source has achieved to extract 50 keV,

100 s long pulse neutral beam and 80 keV, 1 s high power

neutral beam respectively. The data obtained from ther-

mocouples installed in the calorimeter show beam diver-

gence angle and perveance. Nonetheless, although there are

some deviations between the measured value and the

design value, it represents a big step forward for EAST-

NBI system, following the achievement of 320 mA ion

beam extraction last year.

Acknowledgments This work has been supported by the National

Natural Science Foundation of China (Grant No. 11075183).

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Fig. 6 Beam divergence angle as a function of perveance (50 kV,

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